The present invention relates to a reflection-type overhead projector, and particularly to a reflection-type overhead projector wherein the safety and heat dissipation of a projection head are ensured.
Reflection-type overhead projectors for projecting large transparencies onto a remote screen in a lighted room usually comprise a projection head, a base having a Fresnel mirror used as a stage, and an arm on which the projection head is supported above the base. The projection head has a lamp housing wherein are an illumination lamp, and a projection lens with its associated mirror or prism for projecting an image of the transparency placed on the Fresnel mirror onto the remote screen. During projection, the transparency is placed directly on the Fresnel mirror and illuminated from the upper side thereof by the illumination lamp. The light, after having been transmitted through the transparency, is reflected upward by the Fresnel mirror so as to transmit again the image of the transparency. The projection lens and its associated mirror form an image on the remote screen.
The above-described reflection-type overhead projector usually has the lamp housing formed with a transparent window at its bottom fitted with a transparent glass plate through which the lamp illuminates a transparency placed on the stage. Because of the requirement of illumination light of strong intensity, the lamp usually generates a great deal of heat. The lamp housing prevents this heat from escaping, and so becomes quite hot. In particular, the transparent glass plate, which is directly illuminated by the lamp, attains a surface temperature between 160.degree. C. and 270.degree. C.
There is known a lamp housing which is formed with an opening at the bottom in place of the transparent window fitted with a glass plate. This open-bottomed lamp housing allows easy access of the operator's fingers to the inside thereof, which is hot during and just after the use of the overhead projector. Therefore, there is a danger that the lamp will be touched directly by the operator's fingers and that he will thus burn his fingers.